This change fixes the failure in unit tests, which was caused by
the different exception raised by HelpExit since cliff 3.5.0[1].
[1] 7fdd7cb4c50a33233a7052fc345221cc7b935889
Story: 2010022
Task: 45398
Change-Id: I07e51211befa0296d15e6dbdd726c7a989678183
(cherry picked from commit ca596f05b1)